Constant mechanical efficiency of contractile machinery of canine left ventricle under different loading and inotropic conditions.

Abstract

We have recently proposed that the total mechanical energy generated in each cardiac contraction can be quantified by the systolic pressure-volume area (PVA). PVA is the area in the pressure-volume (P-V) diagram that is circumscribed by the end-systolic and end-diastolic P-V relation curves and the systolic segment of the P-V trajectory. This area has dimensions of energy and comprises the external mechanical work and the elastic potential energy. In the left ventricle of crosscirculated canine hearts, we studied the relation between PVA and oxygen consumption per beat (Vo2) above Vo2 for mechanically unloaded contraction. We assumed that this excess Vo2 is utilized for mechanical contraction by the contractile machinery. The percentage of PVA in the excess V02, both in the same unit of energy, J, would then represent the efficiency of energy conversion from the excess Vo2 to the total mechanical energy in the contractile machinery. We obtained this efficiency in variously loaded contractions in both control and enhanced contractile states with epinephrine and calcium. We found that the efficiency was constant at 30-50 (mean 40) % regardless of the changes in both loading conditions and contractile states. By this constant efficiency and a variable fraction of external work in PVA, we accounted for the load-and contractility-dependent variability of the conventional mechanical efficiency (0-30%) of the heart. Key Words; cardiac mechanics, cardiac energetics, pressure-volume area, external mechanical work, potential energy.The efficiency of conversion of energy in a system is the ratio of the useful energy deliverted by the system to the energy supplied to it. In the heart, the conventional mechanical efficiency is the ratio of the external mechanical work to the total energy supplied to the heart (EVANS and MATSUOKA, 1915;SARNOFF

Ventricular energetics in Fontan circulation: Evaluation with a theoretical model

“…Stroke work was approximated by the product of stroke volume (SV) and end‐systolic pressure (Pes). Ventricular efficiency, defined as the ratio between the ventricular external work and O 2 consumption by the myocardium (VO 2 ), 10 was calculated from the linear relationship of VO 2 to pressure–volume area (PVA): 11–13 …”

Ventriculo-arterial coupling detects occult RV dysfunction in chronic thromboembolic pulmonary vascular disease

“…Ventricular efficiency is defined as the ratio between SW and oxygen consumption (Burkhoff and Sagawa 1986). PVA is a linear surrogate of myocardial oxygen consumption (Suga et al 1980(Suga et al , 1983(Suga et al , 1984. PVA is the total mechanical work performed by the ventricle, calculated from the sum of the external stroke work (SWdetermined from the area contained within the PV-loop) that propels the blood from the ventricle and mechanical potential energy (PEthe area bound by the ESPVR and EDPVR) stored in the ventricle at the end of each contraction ( Fig.…”

Effect of reduced aortic compliance on cardiac efficiency and contractile function of in situ canine left ventricle.

“…15 Myocardial efficiency, defined by the relation between total pressure-volume work (pressure-volume area [PVA]) and oxygen consumption, has also been shown to be little influenced by vascular load or ejection history. [16][17][18] We recently reported that lowering vascular resistance could have positive effects on both contractility and efficiency19; however, the relevance of this finding to in situ hearts ejecting into a stiff vasculature is unknown. Other prior studies have attempted to measure in situ effects of aortic stiffening on cardiac function and energetics by replacing the aorta with an artificial conduit or by physically stiffening the native aorta.…”